At a time when the GOP brand has been suffering, polls put the Jersey Republican’s approval rating at 74 percent.

Not a bad place to be when you’re running for re-election.

Christie got these numbers by taking tough stands that people said were impossible and making tough decisions his predecessors put off. So count us among those disappointed that he hasn’t used these high approval ratings in another place New Jersey taxpayers could use it: opposing Medicaid expansion.

Instead, Christie recently announced that the Garden State would accept the Medicaid-expansion part of ObamaCare.

He didn’t have to. In the same decision that upheld ObamaCare as constitutional, the Supreme Court also ruled that states couldn’t be forced to accept the administration’s plans to mushroom Medicaid.

But Christie did anyway.

We understand the difficulty. It’s hard for a governor to turn down an offer he says could actually save the state $227 million in the coming year, especially when the program is being promoted as way to bring health-care coverage to as many as 300,000 uninsured residents. Say no, and you can expect the administration, the media and the uninsured to bash you as another heartless Republican who hates the poor.

But some governors have said no anyway. And they’ve done so for sound reasons. Because, like most of the federal government’s giveaways, this one really isn’t free at all.

Under ObamaCare, while the federal government will pay 100 percent of the Medicaid expansion for the first three years, that contribution shrinks to 90 percent down the road with the state picking up the difference. State taxpayers will also eventually pay more as additional people are added to the health-care rolls. (And, by the way, they’ll also pay for the “federal” aid through their own federal taxes.)

In other words, accepting a wholesale expansion invites more fiscal headaches — even if the impact won’t be felt until much later, by future taxpayers and future governors. Surely Gov. Christie knows what that’s like, because he’s had to clean up the mess other governors left him.

We appreciate that it’s no simple thing to turn down what appears to be free money from the feds. But if you can’t do it when your approval ratings are as high as Chris Christie’s, when can you?